The invention relates to a safety belt assembly for motor vehicles as described in the claims in view of the specification.
Safety belts for motor vehicles have long been known. They serve the purpose of restraining passengers of a vehicle in the passenger seats in the event of an accident and so of protecting the passengers from uncontrollable movements in the interior of the vehicle. This greatly reduces the risk of injury to passengers in the vehicle.
Abrupt vehicle deceleration is known to occur in the event of frontal impact. Since motor vehicle passengers with belts fastened are not rigidly connected to the vehicle or the vehicle seat, there is a certain time delay between vehicle deceleration and passenger deceleration. The greater this time delay, the greater is the stress to which the passenger is subjected. This time delay is determined essentially by slack belt lengths.
Various safety belt assemblies are known which have electronically actuatable belt tightening devices for prevention of slack belt lengths. In these assemblies the severity of an accident is detected by means of sensors and is evaluated in a control unit. The belt-tightening device is appropriately activated by the control unit immediately after the beginning of an accident when a specific accident severity value is reached. As a result, the vehicle passenger is immobilized in his seat a few milliseconds after the accident begins. The danger of slipping beneath the pelvic section of the safety belt and striking the head, against the steering wheel for example is also reduced. The faster and more securely the passenger are immobilized in the vehicle seat; the lower is the risk of injury to the passenger. These remarks apply equally to an accident involving side impact.
A safety belt normally is fastened to three anchor points on the vehicle body. Generally the position of these anchor points remains unchanged during the entire course of an accident in a frontal or rear impact, unless the vehicle body is damaged in the area of the B columns.
The danger that the B column of the vehicle body will be damaged during an accident exists chiefly in the event of a side impact by another vehicle or of a rollover. In these cases the B column often buckles and as a result is displaced relative to the rest of the vehicle. Such displacement is accompanied by change in the relative position of the anchor points of the safety belt, this resulting in recurrence of slack belt lengths. Since the belt-tightening device operates only for a relatively brief period and actuation takes place for the most part immediately at the beginning of an accident, slack belt lengths may recur as the accident proceeds. The vehicle passenger is then no longer immobilized in his seat because of such repeated belt loosening, this leading to the consequence already described that the risk of injury is greatly increased.
DE 195 22 684 A I discloses a device for prevention of belt loosening in which device the shoulder belt section of the safety belt is controlled by a guide integrated into the vehicle seat. This guide comprises a clamping mechanism which may be actuated in the event of an accident and when actuated immobilizes the shoulder belt on the vehicle seat. Displacements of the anchor point of the shoulder belt relative to the vehicle seat occurring, as an accident progresses no longer cause belt length loosening with this device. Consequently, the vehicle passenger remains immobilized in his seat. However, this device requires costly modifications of the vehicle seat, which present a disadvantage from the optical viewpoint as well. Vertical adjustment of the shoulder belt is also no longer possible, since the position of the guide in the vehicle seat is assigned in advance as an invariable.
Reference DE 42 17 969 C2 discloses a belt tightening device with a multistage ignition drive. This belt tightening device permits delayed actuation of a plurality of explosive charges in succession. The time delay, however, performs the function exclusively of restricting belt restraint force. The second actuation cannot be effected independently of the first; it always occurs immediately and necessarily after the first actuation.
The object of the invention is to create a safety belt assembly for motor vehicles which does not present the disadvantages indicated above, which prevent loosening of belt lengths in particular as an accident progresses, an assembly which is simple to produce by cost-effective means.
The essential idea of the invention is represented by design of a safety belt assembly such that the safety belt may be tightened twice in succession by actuation of a belt-tightening device. The second actuation of the belt-tightening device prevents loosening of lengths of the belt, which may occur as an accident progresses.
Relative displacement of the anchor points of the safety belt is detected by at least one sensor mounted on the B column of the vehicle body.
In order to limit for the sake of safety the strain on a passenger in a vehicle by a second actuation of the belt-tightening device, a belt force limiter is provided on the safety belt; it sets a maximum value for belt force.
Inasmuch as belt tightening devices which may be actuated only once are highly complicated in structure, and this applies to a far greater extent to belt tightening devices which may be actuated twice, in a simpler embodiment of a safety belt assembly provision is made for replacement of the belt-tightening device, which may be actuated twice with two separate belt-tightening devices of conventional design.